Visualization of low contrast anatomy and small implanted reference marker "seeds" in electronic portal imaging will be dramatically improved by eliminating the noise effects of scattered radiation "direct hits", and achieving the high signal-to-noise ratio inherent in CCD sensors. A high-performance portal imaging system will be a key factor in reducing localization problems, thereby contributing to lower recurrence of tumors at the margins of the treatment field. an imaging system will be assembled using high density metal-phosphor converter as the sensor and a CCD for read out. The CCD will provide signal-to-noise ratio 3-5 times greater than possible with video tubes at a much lower cost than flat panels. We will perform tests to demonstrate spatial resolution, signal-to-noise ratio, and detective quantum efficiency benefits in comparison to that of conventional system based on metal/ phosphor and electron beam video tube technology. PROPOSED COMMERCIAL APPLICATION: The improved contrast and level of detail visualization provided by the proposed Electronic Portal Imaging Device will accelerate the use of this technology, permit more complex and accurate procedures, and reduce the cost, such that virtually 100% of new radiation therapy systems will be equipped with such a portal imaging device.